Design And Synthesis Of Nanocomposites For Environmental Remediation

Nanotechnology has provided several advanced methods for environmentalremediation, including photocatalytic technology, absorption technique andnanofiltration technology. Recent reports have demonstrated that macroscopicmembranes consisting of TiO₂nanofibers are functional environmental remediationmaterials as recyclable photocatalysts, advanced absorbents, and high efficiency filters.Furthermore, magnetic hollow structures are attractive adsorbents because of their lowdensity, high specific area, recoverability and rich surface functional groups. In thisthesis, we attempt to improve the procedures for fabrication of TiO₂nanofibermembranes and magnetic hollow structures, and couple them with differentnanomaterials （carbon, metal, and semiconductor） to enhance their functionalities,including photo/photoelectric property, adsorbality and selective permeability. Finally,we explore their application in environmental remediation. These results were brieflydescribed as follows:（1） A liquid-liquid interface process for fabricating TiO₂nanofiber membrane withhigh photocatalytic activity: a membrane consisting of TiO₂nanofibers was successfullyfabricated through a simple solvothermal water/n-hexane interface reaction betweentetra-n-butyl titanate and NaOH, followed by post treatments of acid washing andcalcination. Tetra-n-butyl titanate reacts with NaOH at the interface to form high-qualitynanofibers with lateral dimensions below200nm and longitudinal dimensions ofseveral tens of micrometers. The membrane is formed by the interpenetration andoverlapping of the flexible nanofibers and distributed by holes with sizes ranging fromseveral tens of nanometers to several hundreds of nanometers. Because of the porousstructure, this nanofiber membrane exhibited a high efficiency in thephotodecomposition of dyes in water.（2） One-pot growth of free-standing CNTs/TiO₂nanofiber membrane for enhanced photocatalysis: we report a one-pot route to the formation of free-standing, large-areaCNTs/TiO₂nanofiber membrane with enhanced photocatalytic activity. Tetra-n-butyltitanate was reacted with NaOH to form high-quality titanate nanofibers with diametersbelow200nm and longitudinal dimensions of several tens of micrometers. CNTs werecondensed with the as-prepared nanofibers and enabled the nanofibers to assemble intoa free-standing membrane with a diameter of1.5cm. It is proposed that the CNTs act asthe linkers between the nanofibers, and it is crucial for the formation of the membraneunder the hydrothermal conditions. Benefiting from the introduction of CNTs, theas-prepared nanofiber membrane exhibited higher photocatalytic activity than pure TiO₂nanofibers.（3） GO assisting production of a free-standing titania nanofiber membranes withselective permeability and cleaning performance: we report the direct production offree-standing titanate and TiO₂nanofiber membranes with selective permeability andcleaning performance. The membrane was prepared through the hydrothermal reactionsamong tetra-n-butyl titanate, graphene oxide and NaOH. Tetra-n-butyl titanate reactedwith NaOH to form high-quality nanofibers with lateral dimensions below100nm andlongitudinal dimensions of several tens of micrometres. Graphene oxide was condensedwith the nanofibers and enabled the nanofibers to organize into a free-standingmembrane with a diameter of1cm. Interestingly, the interlayer of the as-preparedmembrane stood parallel and as closely packed nanofibers, totally different from thedisorders of those prepared by the filtration method. Benefiting from the distinctivestructure, the nanofiber membrane showed a selective permeability: water could cross iteasily while organic dyes and bacteria were trapped for a long time （120h formethylene blue and methyl orange and24h for rhodamine B and Bacillus coli）.Furthermore, the membrane showed a high efficiency in the photodecomposition of thetrapped dyes because it combined the photocatalytic activity, the porosity, and thecapability of separating photogenerated electrons and holes. Consequently, themembrane possesses both the separation function and cleaning function and should findpotential applications in membrane-based water purification.（4） TiO₂nanofiber coated NiO-Ni foam with cleaning and separation function:Through the precoating of TiO₂on Ni foam and the subsequent hydrothermal reaction of the coating with NaOH and tetra-n-butyl titanate, we successfully demonstrated theengineering growth of TiO₂nanofibers on NiO-Ni foam. The adsorption andphotodecomposition of rhodamine B in water demonstrate that the resulting foamexhibits great convenience in the purification of contaminated water. The selectivepermeability of Au nanoparticles with different sizes reveals that the modified foampossesses size-dependent separation function.（5） Ternary ZnO/ZnS/γ-Fe₂O₃hollow sphere with surface hole.Microwave-enhanced rapid synthesis, bifunctional property, and immobilization ofserum protein: we report a simple and rapid microwave irradiation method to growternary ZnO/ZnS/γ-Fe₂O₃hollow spheres on a large scale; the reaction period onlyrequires30min. The hollow spheres are composed of numerous ZnO, ZnS, and γ-Fe₂O_<sub>3crystallites and the mechanism responsible for their formation is Ostwald ripening.Every hollow sphere has a distinct surface hole: the pore size of some holes is close tothe diameter of the sphere and the others is only tens of nanometers. These hollowspheres have integrated the superparamagnetism of γ-Fe₂O₃and the photoluminescenceproperty of ZnO and ZnS, and hence they can be manipulated by the magnetic force andact as the promising multifunctional platform in biomedical research. Furthermore,since the pore size of the hole on the surfaces of the hollow spheres is large enough toaccommodate BSA molecule with a giant size, the hollow spheres can not only adsorbBSA with their external surfaces but also trap the proteins in their interiors. Theinvestigations on the releasing behavior of BSA by the hollow spheres reveal that BSAmolecules on the external surfaces of the spheres are desorbed quickly, while thoseconfined in the interiors of the spheres are released smoothly and the process issustained over10days. Consequently, the ZnO/ZnS/γ-Fe₂O₃hollow sphere should bethe potential candidate for the immobilization and releasing of biomolecules with giantsizes.